Some construction vehicles such as the wheel loaders include so-called an HST (Hydro-Static Transmission). In travelling, the HST is configured to cause an engine to drive a hydraulic pump and drive a hydraulic motor for travelling (hereinafter referred to as the travelling hydraulic motor) by means of the pressurized oil discharged from the hydraulic pump.
For example, Japan Laid-open Patent Application Publication No. JP-A-2004-144254 describes an exemplary HST system of a 1-pump 1-motor type. Further, Japan Laid-open Patent Application Publication No. JP-A-H11-230333 describes an exemplary HST system of a 1-pump 2-motors type.
The aforementioned HST-type construction vehicles travel at the maximum vehicle speed when a travelling load is minimized while an accelerator pedal is fully pressed down.
Further, the construction vehicles allowed to travel on the public roads are designed to travel within a vehicle speed limit (normally specified in the respective countries and regions, for instance, 38 km/h) even when reaching the maximum vehicle speed.
It should be noted that Japan Laid-open Patent Application Publication No. JP-A-2004-144254 describes a configuration that an operator is allowed to change the lower limit of the displacement of the travelling hydraulic motor for arbitrarily changing the maximum vehicle speed of the construction vehicle in accordance with an operator's intention. In this case, the construction vehicle is still designed to travel within the vehicle speed limit even when reaching the maximum vehicle speed.